“If the patient can’t sleep, ask them if they need pain-killers.” This kind of usage is perfectly acceptable, especially in spoken texts and everyday language.
To non-natives, this use of a plural pronoun (they or them) to refer to a single individual can feel as if it is grammatically incorrect. But it’s fine. Helpful even.
- it’s inclusive and gender-neutral, avoiding the need to endlessly repeat the subject (“person” or “patient” or “party” or whatever)
- it also lets you avoid ugly monstrosities such as he/she and him/her, which really grate when they turn up in the same document for the umpteenth time
- modern and natural
- less long-winded and more readable
There would have been strict grammarians in the past in the English world insisting it was wrong too, conveniently ignoring the fact that it’s been in common use since at least Shakespeare’s day. Victorians loved trying to apply logic to language.
Prevalence: — (not given as this post is, unusually, about something that’s correct)
Frequency: — I will however note that we regularly get our English “corrected” on this point by non-natives who are convinced they know better.
Native: — There is some debate about how far you can go with this approach, for instance in legal texts, but not really about the principle.